This invention relates to sewing machines and, more particularly, to a sewing machine drive motor speed control system.
When operating a motor driven sewing machine, it is desirable to be able to start and stop the drive motor of the sewing machine while having both hands available for guiding the work piece being sewn. One way of accomplishing this objective is to provide a foot or knee operated motor controller wherein the speed of the sewing machine drive motor is controlled by controlling the amount of pressure applied to the controller.
An alternative to the above is fully disclosed in U.S. patent application Ser. No. 907,459, filed May 19, 1978, now U.S. Pat. No. 4,150,634 and assigned to the assignee herein. In the system disclosed in the referenced application, contact switches are provided in close proximity to the stitch forming location of the sewing machine. Means are provided for allowing the sewing machine operator to select an operating speed of the sewing machine drive motor and the sewing machine is operated at that speed when the operator applies hand pressure to the contact switch. Since the contact switch is in close proximity to the stitch forming location, the sewing machine operator may utilize both hands for guiding the work piece being sewn while at the same time controlling the operation of the sewing machine. A disadvantage of such a system is that the sewing machine operator may experience some inconvenience when sewing starts immediately at a fast speed. It would be preferable for the sewing machine drive motor to gradually increase in speed whenever the operator starts sewing.
It is therefore an object of this invention to provide a motor speed controller for fixed speed operation of a sewing machine wherein there is a gradual acceleration of the motor to the fixed operating speed.